For everyone else

Apps and web services communicate with each other over the Internet by sending and receiving 'documents' of data. Here's an example of the kind of data Pokémon Go might download about nearby pokémon from its servers:

Before you can toss a pokéball or swipe right on a cutie, each app needs to translate the downloaded data into a structured representation so it can be filtered, transformed, or displayed graphically. For example, Pokémon Go might want to ignore nearby pokémon that are too strong for your character to catch, then show pictures of the remaining pokémon on a map. Tinder might prioritize recently active matches to increase your chances of matching with someone while they're using the app.

The structured representation, also known as the type of the data, is what allows the app to 'ignore', 'show pictures', 'prioritize', or do anything else meaningful with the downloaded data. The programmers building these apps must write code to represent the types of data the app expects to work with, then convert the downloaded data into those types. Here's an example of what the type of the nearby pokémon data looks like in a popular programming language:

This is not difficult code for a programmer to write--in fact, it's trivial and boring! That's where quicktype comes in.

Given sample data, quicktype automatically derives its type and writes the code needed to work with that data. It writes the boring code for the programmer, so she can save time and focus on the interesting code instead. Neat!